1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member. More particularly it relates to an electrophotographic photosensitive member having a photosensitive layer containing an azo pigment with a specific structure. The present invention is also concerned with an electrophotographic apparatus, a device unit and a facsimile machine that have such an electrophotographic photosensitive member.
2. Related Background Art
Hitherto known organic photoconductive materials used in electrophotographic photosensitive members include photoconductive polymers as typified by poly-N-vinylcarbazole and low-molecular organic photoconductive materials such as 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, and also those comprising a combination of such organic photoconductive materials with all sorts of dyes or pigments.
The electrophotographic photosensitive members making use of the organic photoconductive materials have the advantages that they can achieve a very high productivity and are relatively inexpensive, and besides have the advantages such that wavelength regions to which they have sensitivity can be freely controlled by appropriately selecting dyes or pigments to be used. They accordingly have been studied extensively. In particular, the evolution of functionally separated photosensitive members comprising a lamination of a charge generation layer containing what is called charge-generating material such as an organic photoconductive dye or pigment and a charge transport layer containing a charge-transporting material has brought about a remarkable improvement in the sensitivity and durability to which conventional organic material electrophotographic photosensitive members have had a weakness.
Among the organic photoconductive materials, many of azo pigments are capable of showing superior photoconductivity. Moreover, compounds with a variety of properties can be relatively readily obtained according to the manner by which an azo component and a coupler component are combined. Thus, a large number of compounds have been hitherto proposed. As coupler components used in such azo pigments, the Naphthol AS compounds as disclosed in Japanese Patent Application Laid-open No. 47-37543, etc., the benzcarbazole compounds as disclosed in Japanese Patent Application Laid-open No. 53-95033, etc., the naphthalimide compounds as disclosed in Japanese Patent Application Laid-open No. 54-79632, and the perylene compounds as disclosed in Japanese Patent Application Laid-open No. 57-176055 are known in the art.
However, with a demand for higher image quality and higher durability in recent years, studies are made on a electrophotographic photosensitive member having a higher sensitivity and having a superior electrophotographic performance when repeatedly used.